Keysight Technologies
Measuring the Burst Time-Gated
Power Signal of Wireless Technologies
Using Keysight Power Sensors
For TDMA, GSM, WiMAX™, WLAN, and LTE devices
Application Brief
Introduction
Measuring pulse, burst, or modulated signals for wireless technologies such as TDMA, GSM,
WLAN, WiMAX, and LTE is very important because it is part of functionality testing and power
amplifier module verification during the manufacturing process. High-performance, and average
and peak power meters and power sensors are required for measuring the average power and crest
factor (peak-to-average ratio) of modulated signals throughout various research and development
stages and the manufacturing verification process. To measure the average power of a time-gated
pulse or burst signal in a specific timeframe, a lower cost solution is sufficient.
As this application note illustrates, the compact Keysight Technologies, Inc. U2000A Series USB
power sensor is a low cost solution for measuring the average and time-gated average power
of burst signals. The Keysight U2020 X-Series USB peak and average power sensor is a high
performance USB power sensor with additional 30 MHz video bandwidth capability for measuring
average, peak, and peak-to-average power burst signal. Both USB power sensors series allow the
power measurement to be displayed on a PC and provide the same functionality and performance
as conventional average power and peak power meters and sensors.
In this paper, we pick one of the wireless technologies; timeslot burst structure signal, GSM (Global
System for Mobile communication) for reviewing.
This application note applies to the following products from Keysight
–– U2020 X-Series USB peak and average power sensor
–– U2000A Series USB average power sensor
Methodology
This demonstration shows the power measurement of the GSM timeslot burst signal
structure. The GSM burst signal consists of eight timeslots (slots 0 to 7) each having
a 4.613 ms frame duration and a duration of 577 μs (see Figure 1). The GSM signal can
be transmitted using the same carrier frequency simultaneously, occupying different
timeslots. In other words, each GSM timeslot can be turned on and off, allowing the
transmission to be used to verify the functionality of power amplifier module.
4.613 ms time frame duration
577 µs timeslot duration
Figure 1. GSM timeslot pattern with timeslot 0 On
Using a USB average/peak power sensor to measure the GSM timeslot (with GSM
timeslot 0 On) provides 447 μs for gated duration after having 80 μs offset at the rising
edge of the signal and 50 μs offset at the falling edge of the signal (see Figure 2). This
ensures that the measurement is not affected by the trigger jitter and settling time of
the USB average/peak power sensor.
Time-gated
average power
447 µs
80 µs falling
edge
50 µs falling
edge
Ext triggering
TTL signal
Figure 2. Measuring GSM timeslot 0 with USB average/peak power sensor
Measuring Time-Gated Burst Power
A USB average/peak power sensor offers two triggering mechanisms to perform the
average time-gated burst power measurement: external and internal. Both triggering
mechanisms allow the gate offset (rising edge), and gate length (time-gated duration)
to be specified. Once set, configure the USB average/peak power sensor in gated
mode to perform the measurement.
External triggering
External triggering requires a trigger signal that comes from other instruments via the
sensor’s built-in TTL-compatible trigger input. The USB average/peak power sensor
has built-in trigger circuitry that controls the timing of a pulse-signal capture to enable
measurement synchronization with an external instrument or event. An external signal
greater than 1.9 V applied to the TRIG IN of a USB average/peak power sensor triggers the power sensor to start capturing the measurement.
3
Measuring Time-Gated Burst Power (cont’d)
Internal triggering
With internal triggering, an adjustable measurement-dependent threshold is used
to define the trigger point of the signal being measured. This is especially useful for
measuring pulses that do not occur at fixed intervals. Internal triggering does not
require an external triggering signal to trigger the power sensor to start capturing the
measurement.
Test Configuration and SCPI Commands
Figure 3 and Figure 4 illustrate the measurement configuration when using external
and internal triggering respectively.
Figure 3. Simple setup diagram of a time-gated burst power measurement with a USB average/peak power sensor’s external triggering mechanism
Figure 4. Test setup when using the USB average/peak power sensor with internal trigger to measure the burst-gated signal of a power amplifier module
4
Test Configuration and SCPI Commands (continued)
Measurement data is acquired using the following SCPI commands.
SCPI
Description
Keysight ESG/MXG/EXG signal generator
SYST:PRES
Preset the instrument to its default settings
FREQ 1GHZ
Set frequency to 1 GHz (example)
POW:LEVEL 0DBM
Set output power to 0 dBm (example)
OUTP:MOD:STAT ON
Turn on modulation signal
OUTP:STAT ON
Turn on RF output
For ESG signal generator only
SOUR:RAD:GSM:STAT ON
Recall GSM burst signal waveform
SOUR:RAD:GSM:BURST:STAT ON
Turn on GSM burst signal waveform
For MXG/EXG signal generator only
SOUR:RAD:ARB:WAV \”WFM1:GSM_BURST_WFM\”
Recall GSM burst signal waveform
*OPC?
Wait for operation to complete. A return of 1 means the operation
has been completed
SOUR:RAD:ARB:STAT ON
Turn on GSM burst signal waveform
ROUT:CONN:EVENT1 M2
Set triggering event to Event1
For U2020 X-Series USB peak power sensor and U2000A Series USB average power sensor only
SYST:PRES
Preset the instrument to its default settings
SENS:FREQ 1GHZ
Set frequency to 1 GHz (example)
SENS:AVER:SDET OFF
Turn off the step detector
SENS:DET:FUNC NORMAL
Set measurement to Normal mode for burst-signal power measurement
TRIG:SOUR EXTERNAL
Set triggering source to “EXTERNAL”
Note: If triggering source is “INTERNAL”, execute below SCPI
TRIG:SEQ:LEVEL –20 (example –20 dBm)
SENS:SWEEP:OFFSET:TIME 80u
Set offset time duration of burst signal upon triggering to 80 us
(example)
SENS:SWEEP:TIME 447u
Set sweep time duration of burst signal to 447 us (example)
SENS:AVER:COUNT 1
Set average count to 1 (example)
INIT:CONT OFF
Set to Single Trigger mode. In this mode, return the measurement
using READ?
SENS:MRATE FAST
Set measurement speed to Fast mode to improve the
measurement speed.
Note: Applicable for U2020 X-Series USB peak power sensor only.
(The default speed mode is Normal)
CALC:FEED \”POW:AVER ON SWEEP\”
Set Input Measurement mode to time-gated average power
READ?
Query time-gated average power
For U2020 X-Series USB peak power sensor only
CALC:FEED \”POW:PEAK ON SWEEP\”
Set Input Measurement mode to time-gated peak power
READ?
Querying time-gated peak power
CALC:FEED \”POW:PTAV ON SWEEP\”
Set Input Measurement mode to time-gated peak-to-average power
READ?
Querying time-gated peak-to-average power
5
Conclusion
The low-cost U2000A Series USB power sensor and high performance U2020 X-Series
USB peak and average power sensor support internal and external triggering, making
it easy to measure the necessary pulse, burst or modulated signals for wireless
technologies such as TDMA, GSM, WLAN, WiMAX, and LTE.
References
–– Keysight U2000 Series USB Power Sensor GSM Timeslot Burst Power
Measurement, application note, literature number 5990-4447EN.
–– Keysight U2020 X-Series USB Peak and Average Power Sensor, demonstration
guide, literature number 5991-1221EN.
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06 | Keysight | Measuring the Burst Time-Gated Power Signal of Wireless Technologies Using Keysight Power Sensors - Application Brief
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© Keysight Technologies, 2013 - 2014
Published in USA, August 3, 2014
5991-2642EN
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